Process for coagulating neoprene dispersions by means of magnesium salts



Patented Sept. 25, 1945 PROCESS FOR COAGULATING NEOPRENE DISPERSIONS BY MEANS OF MAGNESIUM SALTS Albert 8. Carter, Wilmington, Del., and Thomas G. Webber, Woodbury, N. 1., assignors to E. I. du Pont de' Nemonrs a Company, Wilmington, Dci., a corporation of Delaware No Drawing. Application Jane 21, 1941, Serial No. 899,226

8 Claims.

This invention relates to the coagulation of latex-like dispersions of neoprene. More particuiarly, it relates to the coagulation of such dispersions wherein the dispersing agents are products obtained by treating rosin and hydrogenated rosin with excess caustic and the coagulating agents are magnesium salts.

Many theories have been advanced to account for the phenomenon of coagulation of dispersions. Also, many materials are known to have greater or lesser coagulating effects on both natural and synthetic dispersions. No theory will account for i the action of all coagulants or for the variation in the action of coagulants on various dispersions. It has been found that, for some purposes, neoprene (modified or unmodified polymeric 2-- chloro-1,3-butsdiene) can best be made by polymerizing an emulsion of 2-chloro-l,3-butadiene and thereby obtaining a latex-like dispersion of polymer. The dispersion is then coagulated and the neoprene obtained in suitable form for further use. Coagulation can be elected by freezing type is unduly water absorptive after curing.

It is an object of this invention to produce a cured neoprene having improved resistance to water absorption. Another object is to produce a water-resistant neoprene from a dispersion of neoprene wherein the dispersing agent is a product obtained by treating a member of the group consisting of rosin and hydrogenated rosin with excess caustic. A further object is an improved method of coagulating such dispersions of neoprene. Other objects will appear hereinafter.

V It has been discovered that these objects can be accomplished by the use of water-soluble magnesium salts, and especiallymagnesium sulfate,

as the coagulating agent.

In order that the process may be more fully understood, the following specific example is given by way of illustration, but the invention is not limited thereto as hereinafter.

' Example The late: to be mandated was prepared ls foiwill become more apparent lows: Chloroprene (100 parts) containing 0.6 part of sulfur'and 4 parts of'rOsln was emulsified by mechanical agitation in 227 parts of water containing 0.5 part of ammonium persulfate, 0.8 part of sodium hydroxide and, 0.5 part of the sodium salts of the dinaphthyl methane sulfonic acid prepared according to U. 8. Patent No. 1,336,759. The resulting dispersion was kept at 40 C. in a suitable vessel which could be externally cooled and heated until the density ceased to increase, indicating that the polymerization was substantially complete. The resulting latex was then stabilized with 2.5 parts of tetra ethylthiuram dlsulflde and was then agitated with 111 parts of a 3- per cent aqueous solution of hydrated magnesium sulfate, (MgSO4.'lH=O) which caused complete coagulation. The coagulum was then washed free from the excess of magnesium sulfate by passage through a rubber with corrugated rolls under a spray of fresh water. The

' excess of magnesium sulfate was thus rapidly removed, the dispersing agents having been converted into insoluble salts which remained in the polymer. The washing step was, accordingly, much shorter than in earlier processes where the dispersing agents had to be washed out. The polymerv was then dried by milling on a rubber mill with smooth rolls in the usual manner.

The mechanical feature of the operation was still more conveniently carried out, however, .ac-

cording to the method disclosed in the copending U. 3. application of Wanderer, Serial No.

362,557, filed October 24, 1940. According to this method, the dispersion of chloroprene polymer and the solution ofmagneslum sulfate were fed simultaneously and continuously into a hopper in which coagulation tool: placeand from which it dropped into the large rend of a chamber, in the form of a truncated cone in which a rotating into another extruding machine,- similar to the first, in which it was brought into contact with continuously added fresh water by the action of the rotating worm which stretched and tore the material and thus presented fresh surfaces to the action to the water. The washed material was then extruded in a continuous form as. from the first apparatus and was further driedby passing through two additional extruding machines to V which no water wasadded. From the last of 3 continuous, nearly dry, threads.

these, the product was delivered in the form of m The residual water was readily removed by passing the threads continuously through a drying turmel counter-.

current to a stream of warm air. The dried poly- I mer, prepared by either of thesemethods (100 parts by weight), when compounded with 7 parts of magnesium oxide and parts of zinc oxide and cured, gave a stock which increased only 8.1

per cent in volume when immersed in the water at 100 C. for 2 days.

A water absorption of 7.2 per cent was obtained when the latex was acidified with dilute acetic acid before the coagulation by magnesium sulfate, but was otherwise treated as in the example.

For comparison, samples of the same latex as was used in the example were coagulated by other 3 methods. The first method used was that preferred in U. 8. Patent 2,187,146. According to this, the latex was frozen in the form of a thin layer upon the periphery of an internally cooled drum rotating and partly immersed in the latex," the frozen layer was removed from contact with the unfrozen latex and maintained in contact with the cooled drum until coagulation was com- I plete, then removed and warmed to melt the ice.

When the resulting thin, continuous sheet of coagulum was washed and dried as such or when worked up by the method of Wanderer above described, and then, in either case, compounded and cured as above, the water absorption was definitely higher (12.8 per cent) than when the much simpler coagulation method of the present invention (giving 8.1 per cent absorption) was used. A sample of the latex coagulatedby adding solid sodium chloride, then washed and dried by the method of Wanderer, and compounded and cured; gave a water absorptionof 45 per cent.

Furthermore, a quantity of a per ,centsolution of sodium chloride equal to that of the latex was required for eilicient coagulation, as compared with one-third of the quantity of a 3 per cent solution ofmagnesium sulfate used in the example.

It will thus be seen that the present invention provides a method for coagulating dispersionsof neoprene which, in comparison with the prior art, is cheaper and simpler and gives a product which requires less subsequent treatment.

The term "emulsifying agent obtained by treating a member of the group consisting of rosin and in-water to a dispersion of solid-in-water. The

rosin derivatives are much more'eil'ective in the liquid-in-water system than in the solid-in-water system, while the said sulfonic acids are more effective inthe solid-in-water system; i. e., the

' dispersion of chloroprene polymer. The presence of the said sulfonlc acid salts, therefore, greatly aids the stability ofthe chloroprene polymer system, and is extremely desirable where the dispersion is acid or is acidified before coagulation. Accordingly,,in its preferred form, the present invention is directed to the coagulation of dispersions of neoprene wherein both a rosin derive "'ative and a sodium salt of a sulfonic acid of an alkylated naphthalene are present. This is illustrated in the example.

We may use, as coagulating agents, any magnesium salts which are capable of giving aqueous solutions of a concentration of l per cent or more at the temperature at which the coagulation is carried 'out. Thus, magnesium chloride, magnesium nitrate, and magnesium acetate-may be used to good advantage, although we prefer magnesium sulfate, both because of its availability and cheapness andits emciency. The quantity of magnesium salt used should, preferably, lie

between that theoretically required to react with all thedispersing agents and the excess of caustic present and twice this theoretical quantity, although less than the theoretical quantity will cause coagulation. Very large quantities of the salt, in addition to being unnecessary, tend to be retained in the coagulum and require a, longer "washing for their removal. Suitable concentrations of the magnesium salt in the solution added have been found to lie between 1 and 5 per cent. When a more dilute solution is used the total volume of liquid to be handled is unnecessarily increased; on the other hand, with a, more concentrated solution, the salt isless effectively used. The temperatures at which the. coagulation is carried out is not critical and may lfe anywhere between the freezing point and boiling point of the system. Convenient temperatures lie between about 20' C. and 40'? 0.; that is, between ordinary temperature and the temperature at hydrogenated rosin with excesscaustic' includes agents so prepared from any type of rosin (such as American or French, gum or wood), or from products derived from any of these by either partial or complete hydrogenation. It also .includes the products obtained without purification, as

well as those resulting through purification of g the abietic. acids in the rosin. .The preferred caustic is sodium hydroxide, although any base capable of dissolving the rosin, .such as potassium and ammonium hydroxides may be used.

' naphthyl sulfonic acid, dinaphthyl methane sulfonic acid, etc. 'As the chloroprene polymerizes, the chargechanges from an emulsion of liq idwhich the dispersion is polymerized.

As in the above example, the principal use'of this invention is to convert the neoprene from the form of an aqueous dispersion to a form in which it is ready for compounding and conversion into articles ofmanufacture. The process may also be used to advantage, howeveti in the forming of articles directly from the latex, That is, the advantage of low water absorption may also be gained if the magnesium salt solutions of the present invention are substituted for the coagul'ating solutions' usedin the art. For example,

the latex may be extruded through a suitable orifice into a solution of the magnesium salt, ac-

cording to the general method described in the 'British Patent No. 393,172, thus forming a continuous thread of high water resistance, Similarly,. articles such as gloves may be made by applying the latex to a suitable mold and then I dipping the mold with the adhering layer of latex into a solution of the magnesium salt. 7

Salts of polyvalent metals other than magnesium, such as zinc sulfate, barium chloride, cobalt chloride, stannic chloride and lead acetates, will also cause coagulation of these neoprene disersions in many cases, but all those which do are either less effective, or give products characterlzed by greater water absorption, instability, or other undesirable properties.

a,sss,ess

It is apparent that many widely diiferent embodiments of this invention may be made without departing from the spirit and scope thereof, and, therefore, it is not intended to be limited except as indicated in the appended claims.

We claim:

1. In a process for making a water-resistant, rubber-like material by emulsifying 2-ch1oro-1,3- butadiene in an aqueous medium by means of a sodium salt obtained by treating a member of the group consisting of rosin and hydrogenated rosin with excess sodium hydroxide, polymerizing the 2-chloro-1,3-butadiene while so emulsified, coagulating the resulting dispersion of polymer and washing and drying the coagulum, the step of coagulating the said dispersion by means of magnesium sulfate in quantity sumcient to react with all the dispersing agent present.

2. In a process for making a water-resistant, rubber-like material by emulsifying 2-chloro- 1,3-butadiene in an aqueous medium by means of a sodium salt of a sulfonic acid of an alkvlated naphthalene and of a sodium salt obtained by treating a member of the group consisting of rosin and hydrogenated rosin with exces sodium hydroxide, polymerizing the 2-chloro-1,3-butadiene while so emulsified, coagulating the resulting dispersion of polymer and washing and drying the coagulum, the step of coagulating the said dispersion by means of magnesium sulfate in quantity sumicent to react with all the dispersing agent present.

3. In a process for making a water-resistant, rubber-like material by emulsifying 2-chloro-1,3- butadiene in an aqueous medium by means of a sodium salt obtained by treating a member of the group consisting of rosin and hydrogenated rosin with excess sodium hydroxide, polymerizing the 2-chloro-1,3-butadiene while so emulsified, coagulating the resulting dispersion of polymer and washing and drying the coagulum, the step of coagulating the said dispersion by adding thereto an aqueous solution of about 1 to 5 per cent concentration of magnesium sulfate in quantity sufilcient to react with all the dispersing agent present. a

4. In a process for making a water-resistant, rubber-like material by emulsifyin 2-chloro-l,3- butadiene in an aqueous medium by means of a sodium salt of a sulfonic acid of an alkylated naphthalene and of a sodium salt obtained by treating a member of the group consisting of rosin and hydrogenated rosin withexcess sodium hydroxide, polymerizing the 2-chloro-L3-butadiene while so emulsified, coagulating the resulting dispersion or polymer and washin and drying the coagulum, the step of coagulating the said dispersion by adding thereto an aqueous solution of about 1 to 5 per cent concentration of magnesium sulfate in quantity suilicient to react with all the dispersin agent present.

5. In a process for making a water-resistant, rubber-like material by emulsifying 2-chloro-l,3-- butadiene in an aqueous medium by means of sodium rosinate, polymerizing the 2-chloro-1,3-

' butadiene while so emulsified, coagulating the resulting dispersion of polymer, and washing and drying the coagulum, the step of coagulating the said dispersion by adding thereto an aqueous so-' aqueous solution of about 1 to 5 per cent concentration of magnesium sulfate in quantity sumcient to react with all the dispersing agent.

7. In a process for making a water-resistant, rubber-like material by emulsifying 2-chloro-L3- butadiene in an aqueous medium by means of sodium salt of hydrogenated rosin, polymerizing the 2-chloro-1,3-butadiene while so emulsified, coagulating the resulting dispersionv of polymer, and washing and drying the coagulum, the step of coagulating the said dispersion by adding thereto an aqueous solution of about 1 to 5 per cent concentration of magnesium sulfate in quantity sufiicient to react with all the dispersing agent.

8. In a process for making a water-resistant,

rubber-like material by emulsifying 2-chloro-1,3- butadiene in an aqueous medium by means of sodium salt of dinaphthyl methane sulfonie acid and of sodium salt of hydrogenated rosin, polymerizing the 2-chloro-1,3-butadiene while so emulsified, coagulating the resulting dispersion of polymer, and washing and drying the coagulum, the step of coagulating the said dispersion by adding thereto an aqueous solution of about 1 to 5 per cent concentration of magnesium sulfate in quantity sufiicient to react with all the dispersing agent.

ALBERT S. CARTER. THOMAS G. WEBBER. 

